Investigation of the impact of extraterrestrial energetic particles on stratospheric nitrogen compounds and ozone on the basis of three dimensional model studies

As a result of solar events like Coronal Mass Ejections (CMEs) and solar flares, highly energetic charged particles including protons and electrons can precipitate in the direction of the Earth. Having sufficient energies, these particles can penetrate down to the middle atmosphere and lead to a change in the chemical composition of the atmosphere. In particular during strong events, these charged particles induce an ionisation in the atmosphere that can reach down to the lower stratosphere. This ionisation is followed by a fast positive ion chemistry that causes a strong increase in reactive HOx (H, OH, HO2) an NOx (N, NO, NO2). HOx and NOx constituents eventually destroy O3 in catalytical reaction cycles. Furthermore, NOx is long-lived during polar winter and can be transported into the middle and lower stratosphere, where it can contribute to the O3 depletion. The increase in NOx in the upper and middle atmosphere due to solar events and the consequential depletion of O3 has been observed as during the Solar Proton Event (SPE) in October/November 2003 by satellite instruments. In atmospheric models, the generation of HOx and NOx can be well described by parametrisations to include in neutral models. Whereas other changes, for instance in chlorine compounds, can not be described sufficiently by this parametrisation. The purpose of this PhD thesis is, to investigate the impact of strong solar particle events on the abundance in NOx and O3 in the stratosphere and mesosphere on the basis of threedimensional model studies.For this purpose a three-dimensional Chemistry and Transport Model (CTM) has been extended to the upper atmosphere (lower thermosphere). To include the processes in the mesosphere and lower themosphere a new meteorological data set has been implemented to the model. To describe the ionising effect of energetic particle on the atmosphere, three-dimensional ionisations rates from Atmospheric Ionization Module Osnabrück (AIMOS) were implemented into the model. The previous version of the CTM uses a so-called family approach to solve the chemical equations. This family approach is a appropiate assumption in the stratosphere, but cannot be applied in the mesosphere and thermosphere. To consider chemical processes in the upper atmosphere a non family version of the chemical code have been implemented into the CTM. To investigate the impact of precipitating particles on chlorine compounds, additional parametrisations have been implemented in a case model study from the University of Bremen Ion Chemistry (UBIC) model. With this extended version of the three-dimensional CTM of the stratosphere, mesosphere, and lower thermosphere, different model simulations for the period between 2002-2009 have been performed. This period covered the maximum phase of the 23. solar cycle with several medium and strong SPEs as well as the rather quiet declining phase of cycle 23 and the beginning of cycle 24